This application describes a new and distinct variety of alga named Chlamydomonas reinhardtii, ‘DG8-108’, that can accumulate 2.5 times more biomass on mineral medium and under photosynthesis, compared to wild-type C. reinhardtii, under optimal and stressful environmental conditions. ‘DG8-108’ was developed for use in plant physiological research and in the commercial production of bioproducts.
Chlamydomonas is a genus of unicellular green algae (phylum Chlorophyta; class Chlorophyceae). These algae are found in soil, fresh water, oceans, and even in snow on mountaintops. Algae in this genus have a cell wall, a chloroplast, an “eyespot” that perceives light, and two anterior flagella with which they can swim using a breast-stroke type motion. More than 500 different species of Chlamydomonas have been described, but most scientists work with only a few species.
The most widely used laboratory species is Chlamydomonas reinhardtii (Dang). The wild-type of this species (137-C) was isolated from soil by Dr. Smith in 1948 in USA (see in rf. Levine 1960). Cells of this wild-type variety are haploid, and can grow on a simple liquid or solid medium of inorganic salts, using photosynthesis to provide energy. Cells can also grow in total darkness when acetate is provided as an alternative carbon source. When deprived of nitrogen, haploid cells of opposite mating types can fuse to form a diploid zygospore which forms a hard outer wall that protects it from adverse environmental conditions. When conditions improve (e.g. when nitrogen is restored to the culture medium), the diploid zygote undergoes meiosis and releases four haploid cells that resume the vegetative life cycle.
We used C. reinhardtii variety 137C, which was originally sent to us by Dr. R. P. Levine in 1965, to create the C. reinhardtii variety ‘DG8-108’ described herein to facilitate investigation of general plant physiological phenomena. This novel variety has been created, isolated, cultivated and maintained as a pure algal culture in laboratories in Puschino, Russian Federation.
The novel variety ‘DG8-108’ was created by exposing wild-type C. reinhardtii 137-C to γ-radiation. ‘DG8-108’ cells may be range from 18-25 microns in length, are green in color (nearest color equivalent: Pantone #364; FIG. 1), and have either a spherical and/or ovate morphology. ‘DG8-108’ reproduces vegetatively by longitudinal fission of the cells. ‘DG8-108’ can be cultivated and maintained in agar (plates) or liquid culture. ‘DG8-108’ cultivated and maintained on agar plates with mineral medium form green colonies (nearest color equivalent: Pantone #364) that are 0.3-0.5 cm in diameter within 10 days. The size of individual ‘DG8-108’ cells is 60 to 80% greater than wild-type varieties. The size of ‘DG8-108’ colonies in 1.3-1.8 times greater than the size of wild-type colonies. Adult cells of ‘DG8-108’ have a very large chloroplast that occupies nearly ⅔ of the total cell volume, and the chloroplast has 1.9-2.0 (SD=0.4) times more thylakoid membranes compared to wild-type cells (FIG. 1-A, 1-B; Number of thylakoids calculated on basis of chloroplast cross section surface).
General physiological and specific plant physiological assays of photosynthetic productivity showed that ‘DG8-108’ possess physiological characteristics that distinguish it substantially from wild-type C. reinhardtii varieties. The total photosynthetic productivity of ‘DG8-108’, on both a gross and net basis is, at minimum, 2-2.5 times greater than wild-type (FIG. 2).
The chlorophyll content (chl a+chl b) of ‘DG8-108’ is nearly double that of the wild-type (FIG. 3) and persists even under chronic stress conditions (FIG. 4). The visual color difference between ‘DG8-108’ and ‘wild-type’ C. reinhardtii is due to the increased chlorophyll content of ‘DG8-108’ cells.
In addition, ‘DG8-108’ shows increased stress tolerance (higher pigment content and higher survivorship demonstrated (compared to wild-type varieties) to extreme environmental conditions (FIGS. 4 and 5).